Nowadays, numerous products and product parts are made of composite materials or composites. In order to achieve sufficient strength and stability under load while at the same time keeping the weight low, a fiber composite construction is often used. Under high mechanical loads, however, customary fiber composite parts have a low resistance to abrasion. This limits the durability of these composites and parts made of them.
Components, and particularly blades, made of a fiber-reinforced composite material, which are exposed to a fluid flow in turbo-engines, are particularly endangered by erosion because of abrasive particles in the fluid flow media and by thermal stress. For protecting power unit components, it is suggested, in German Patent Document DE-OS 43 43 904, to apply an erosion-resistant inorganic lacquer layer to the component. Although by means of this process the components can also be repaired, the permanence of the adhesion of the lacquer layer on the components presents a problem. Frequently, during the useful lifetime of the component, the application of the lacquer layer must be repeated.
As an alternative, German Patent Document DE-PS 42 08 842 discusses an erosion protection for helicopter rotor blades made of fiber-reinforced plastic materials. This is achieved through, at the critical points, a rotor blade being covered by a glued-on metal sheet, which is coated with particles of metal compounds. The problem of permanence of adhesion between the glued-on metal sheet and the composite fiber structure situated underneath also exists in this case.
A development by the inventors relates to a blade for a turbo-engine in which at least one blade exposed to the flow is constructed as a composite with layers of fiber-reinforced plastic material and with at least one metallic cover layer, which is applied to part of the surface or to the whole surface, as a protection against erosion. This cover layer has metallic fibers or threads, which are connected with the fiber-reinforced plastic material of the adjoining layers by way of the same synthetic resin binder. In addition, the blade may be coated, over part of its surface or over its whole surface, by an erosion-resistant protective layer, such as a temperature-resistant lacquer or a thermoplastic foil.
In addition to the erosion resistance because of the use of metallic fibers or threads in the cover layer, a tolerance to defects is also reached as a result of the plurality of mutually connected fibers or threads. As a further advantage, for example, in the case of local damage to the cover layer, the automatic spreading of the damage or a detaching of the cover layer is avoided, which may occur, for example, in the case of glued-on metal sheets as the cover layer, discussed above. The advantageous high adhesiveness of the cover layer on the substrate situated underneath is ensured by the joint synthetic resin binder, which connects the fiber-reinforced plastic layers and the cover layers to one another as well as with one another. Furthermore, the electric conductivity of the metallic fibers or threads results in a lightning protection, which is advantageous, for example, for rotor blades or propellers. However, it is desirable to further improve the resistance to abrasion and erosion of a correspondingly constructed composite for applications in the case of extremely stressed components.
For this purpose, the invention provides a composite comprising a substrate having at least one fiber layer, and a cover layer, which adjoins and which, adjacent to the at least one fiber layer, has metallic fibers and/or threads. The at least one fiber layer of the substrate and the metallic fibers and/or threads of the cover layer are saturated with binder or at least one binder composition so that, as a result, the substrate and the cover layer are formed and connected. The improvement of the abrasion resistance to composites constructed according to the present invention is achieved, inter alia, by embedding metallic, ceramic or glass-type particles in the cover layer in the area of the metallic fibers and/or threads.
Embedding particles, according to the invention, into the area of the metallic fibers and/or threads of the cover layer improves the resistance to abrasion. In addition and as another advantage, the added particles result in lower or higher coefficients of friction that can be adjusted in connection with such a composite depending on the application requirement. The electric conductivity of the cover layer is advantageously maintained because of the metallic fibers and/or threads therein. Furthermore, the abrasive behavior of this cover layer is improved in comparison to earlier constructions.
In preferred embodiments of the invention, it is provided that the substrate contains a plurality of fiber layers and/or is a fiber-reinforced plastic material and/or the at least one fiber layer of the substrate completely or partially contains non-metallic fibers.
Generally, in addition to one or several areas with/of metallic fibers and/or threads, the cover layer may also have other components or sections. The cover layer is preferably formed of a substantial amount of the metallic fibers and/or threads, and with the embedded particles and the binder.
Within the scope of another preferred aspect of the composites of the invention, it is provided that the fiber layer and the metallic fibers and/or threads of the cover layer are saturated and connected by means of the same binder. However, as a function of the usage demands of the composite, different binders can be used in the layers. For example, resin, particularly synthetic resin, is suitable for use as the binder or in binder compositions.
The metallic fibers and/or threads of the cover layer of the composite according to the invention may form a mesh and/or a woven structure. However, it is particularly advantageous for these fibers and/or threads to be present in the form of felt.
According to the desired characteristics of the cover layer, metallic, ceramic and/or glass-type particles can be used. In particular, the particles may contain TiC, TiN, TiAl, Fe, steel, Ni, Si, metal alloys, diamond, glass and compounds therewith as well as combinations thereof. With respect to their structural shape and geometry, the particles may be solid, porous or hollow.
In order to facilitate and optimize the introduction of the particles into the area of the metallic fibers and/or threads of the cover layer, it is advantageous for the particles to be components of a carrier medium which surrounds the metallic fibers and/or threads of the cover layer at least partially and/or directly. Such a carrier medium also promotes the distribution capacity and the adhesion of the particles in the area of the metallic fibers and/or threads of the cover layer. Preferred types of carrier medium are solder compounds, metal fillers, adhesive agents, such as bonding agents in particular, or thermoplastic materials.
For a distribution which is as uniform as possible and for a secure fastening of the particles in the area of the metallic fibers and/or threads of the cover layer, it is also advantageous for the particles to be completely or partially connected by means of the binder, optionally the carrier medium, by a mechanical clamping with the metallic fibers and/or the threads of the cover layer, by sintering or the HIP (hot isostatic pressing) process with the metallic fibers and/or threads of the cover layer. However, basically all suitable processes are available within the scope of the invention.
A further development of the composite according to the invention is characterized in that, in comparison to the substrate, the cover layer has a higher resistance to abrasion, a higher fire-proofing capacity and/or a higher electric conductivity. As a result, a cover layer can be used which is optimized according to the physical and chemical requirements.
In order to be able to implement the protection of the cover layer wherever it is required and in order to thus provide a particularly useful and durable composite, it may also be provided that the cover layer is constructed on several sides of the substrate. This embodiment will be particularly preferable if the cover layer surrounds the substrate at least essentially completely.
In addition, the invention provides a process for manufacturing the composites described, which can be used to provide components of improved resistance to abrasion and erosion, especially in the case of extremely stressed components.
This process relates to the manufacturing of a composite which contains a substrate, which has at least one fiber layer, and a cover layer which adjoins the latter and which contains metallic fibers and/or threads at least adjacent to the at least one fiber layer, the at least one fiber layer of the substrate and the metallic fibers and/or threads of the cover layer being saturated with binders and as a result the substrate and the cover layer being formed and connected.
Without being exclusively limited thereto, composites can be produced by means of this process which have the above-mentioned characteristics and the characteristics indicated throughout this disclosure.
According to the process, it is provided that particles are embedded into the cover layer in the area of the metallic fibers and/or threads before the at least one fiber layer of the substrate and the cover layer are saturated with a binder in the area of the metallic fibers and/or threads.
In contrast to the earlier development by the inventors, in the present process no attention has to be paid to an additional surface shaping or layer thickness of a separate protective layer on the otherwise finished composite, which simplifies the manufacturing process and lowers the corresponding expenditures.
Preferably, the particles are provided in a pasty or liquid carrier medium and for embedding the particles, at least in the area of the metallic fibers and/or threads, the cover layer is dipped into this carrier medium or this carrier medium flows through the cover layer.
According to a variant of this embodiment of the process according to the invention for manufacturing a composite, a liquid solution is used as the carrier medium, particularly an alcoholic or alcohol-like solution, such as ethanol. Before the saturation of the at least one fiber layer of the substrate and of the cover layer in the area of the metallic fibers and/or thread with binder, such a carrier medium is then removed while leaving particles on the metallic fibers and/or threads of the cover layer, which can be achieved by evaporating.
Another basic possibility of embedding the particles within the scope of the invention, concerning the metallic fibers and/or threads of the cover layer, consists of using a solder compound, a metal filler, an adhesive agent, particularly a bonding agent, or a thermoplastic as the carrier medium. In this case, during the saturation of the at least one fiber layer of the substrate and of the cover layer in the area of the metallic fibers and/or threads, the carrier medium together with the particles remains with the binder on the metallic fibers and/or threads of the cover layer and therefore forms an at least partial coating over the metallic fibers and/or threads of the cover layer. Preferably, such a carrier medium makes it possible that the correspondingly treated cover layer can still be shaped or adapted to shapes.
As a further development of the above-mentioned embodiments, it can also be provided that, before the contact of the carrier medium with the metallic fibers and/or threads of the cover layer, the particles are loaded into the carrier medium by pressing or sintering.
The carrier medium can generally also be applied or loaded by means of pouring, trickling or spraying onto or into the area of the metallic fibers and/or threads of the cover layer.
The invention also includes a process variant in the case of which the particles are provided in a powder form. Here also, the charging of the particles into the area of the metallic fibers and/or threads of the cover layer takes place in that, at least in the area of the metallic fibers and/or threads for the embedding of the particles therein, the cover layer is dipped into the particle powder or the particle powder flows through it. As an alternative, the particle powder can, for example, also simply be applied to the area of the metallic fibers and/or threads of the cover layer by pouring or trickling. A spraying of the area of the metallic fibers and/or threads of the cover layer with particle powder is also possible if, for example, compressed air is used as a transport medium for the particles.
In the case of the above-mentioned embodiments, the individual particles are then held in the area of the metallic fibers and/or threads in a mechanical or, for example, electrostatic manner. However, within the scope of the invention, other possibilities can also be considered so that, for example, the particles adhere to the metallic fibers and/or threads by the bonding characteristics of the particles or their surface.
Within the scope of the invention, there are numerous possible ways to connect the particles, completely or partially, with the metallic fibers and/or threads of the cover layer by means of the binder, the carrier medium, mechanical clamping, sintering or the HIP-process, for example.
According to a particularly preferred variant of the composite, a felt is produced from the metallic fibers and/or threads of the cover layer, before the particles are placed in it. As an alternative or in addition, for forming the area of the cover layer with the metallic fibers and/or threads, a mesh and/or woven structure can also be formed of them.
A preferred approach in the case of the process according to the invention for producing a composite body consists of saturating the at least one fiber layer of the substrate and the cover layer in the area of the metallic fibers and/or threads in zones with a binder.
In another preferred embodiment of the process, it is provided that a single binder is used for forming the substrate and the cover layer and for their connection. However, in principle, different binders can also be used at different layers in order to meet, as optimally as possible, the requirements of the fiber materials used and/or the required application-based characteristics of the composite and particularly of its cover layer.
In order to largely avoid shaping after-treatments, it is preferred that the saturating of the at least one fiber layer of the substrate and of the cover layer in the area of the metallic fibers and/or threads with the binder be carried out in a mold or in a mold cavity. If the intended use of a composite requires a surface treatment, it can be subjected, particularly, on the cover layer, however, subsequently or basically at any time, on its side facing away from the substrate, after the saturation of the at least one fiber layer of the substrate and of the cover layer in the area of the metallic fibers and/or threads with binder, and particularly after solidification of the latter, as provided according to another process variant.
Additional advantageous and embodiments of the invention will be appreciated by one skilled in the art.